Fuel control apparatus for liquid fuel burners



ug. l0, 1948.

D. BRADBURY EVAL FUEL CONTROL APPARATUS FOR'LIQU'ID FUEL BURNERS Filed Jan. 3l, 1944 Patented Aug. 10, 1948v Donald Bradbury, Meyer, Drexel Prospect Park, and Charles A. Hill, Pa., house Electric Corporation,

Pa., a corporation of Pennsylv assignors to Westin:-

East Pittsburgh, anla Application January 81, 1944, Serial No. 520.564

` z calms. (CL s-3&4)

This invention relates to power plants and particularly to a control system for a gas turbine power plant and it has for an object to provide an improved device of the character set forth.

The present invention, while not limited thereto, is particularly adapted to be used to control a gas turbine power plant like that disclosed in the patent to Stewart Way, No. 2,405,723, issued August 13, 1946, and assigned to the assignee of lthe present invention. A power plant of the type disclosed in the mentioned Way patent includes an air compressor, an air heating apparatus, a turbine, and a propulsion, jet nozzle all housed within a streamlined tubular casing. A plant of this character is particularly suitable for propelling aircraft at high speeds and operates generally as follows: Air enters the forward end of the tubular casing and is'compressed in the compressor, the compressed air is thennheated in the heating apparatus -by combustion of fuel supported by the compressed air. The resulting motive fluid comprising the products of combustion and the excess compressed air drives the turbine and is then discharged through the propulsion nozzle as a jet, the reaction of which serves -to propel the aircraft. The turbine extracts at least sulcient power from the motive fluid to drive the compressor and auxiliaries.

Y The fuel is supplied to the air heating apparatus,

under the control of a throttle valve, by means of a positive displacement pump which is preferably driven -by the turbine.

A power plant of this character is designed to operate at relatively high speeds, for example, 18,000 R. P. M. or more, and it is desirable that means be provided lto prevent dangerous overspeeding of the turbine shaft. Under normal conditions the rotational speed of the turbine shaft is dependent on the rate at which fuel is supplied to the combustion apparatus and in accordance with the present invention the fuel rate is controlled automatically to prevent such dangerous overspeeding.

It is, accordingly, a further object of the invention to provide means for measuring and for limiting the rotational speed of a gas turbine.

' These and other objects are eil'ected by the invention as' will be apparent from the following description and claims taken in connectionwith the accompanying drawings, forming a part of this applica-tion, in which:

Fig. 1 is a. side elevational view of a gas turbine power plant in which the present invention is incorporated. portions of the outer casing structure being broken away to show certain de- 2 tails ofconstruction .and the fuel control and turbine speed governing system of the present invention being shown diagrammatically with the elements thereof in section, and

Fi g. 2 is a longitudinal sectional view of a mod- -iiled form of a control valve which may be employed in the present invention.

' vThe -power plant shown in Fig. 1 comprises in general an outer casing structure I open from end to end and having a central core structure il providing an annular flow passage i2 which extends fore and aft with respect to the aircraft in which it is mounted. The central core structure l I is supported by the casing structure along its longitudinal axis and includes a hollow fairing cone It defining with the forward or left end, as viewed in Fig. 1, of the casing Il the inlet portion of the flow passage I2. The fairing cone houses a fuel pump, generally indicated I5, and other auxiliary apparatus (not shown) and is supported from the casing by hollow compressor guide vanes IG. The core structure also includes a rotor Il of an axial flow ilxed blades of which are carried by the casing I0, a rotor I8 of a turbine 2l and a conicaltailpiece 22 which defines with the rear end of the casing structure a propulsion nozzle 2l. The incompressor I8, the

termediate portion of the core structure between the compressor and the turbine comprises an inner wall structure 24 which houses a shaft Il connecting the turbine rotor i9 and compressor rotor il, and defines with the casing l0v an annular com-bustion chamber 26. The shaft 2i is journaled in suitable bearings 25a carried by the outer casing.

The com-bustion chamber 2i is provided with a suitable burner or burners, such as shown in the copending application of Way et al.. Serial No. 511,468, illed November 23, 1943, and assigned to the assignee of the present invention, for heating the air compressed by the compressor. In the embodiment shown, a plurality of perforated, tapered, burner tubes 2l are mounted in the aunular combustion chamber 26 with their large open ends 2l directed downstream. Fuel under pressure is supplied -to the burner tubes from a manifold pipe 29 connected to a fuel supply as hereinafter described and is fed through branch pipes 3|" to atomizing nozzles 32 extending into the burner tubes through the small closed ends 33 thereof. Suitable means, including spark plugs I4 extending into the burner tubes, are provided for igniting the air-fuel mixture.

rlhe present invention is not concerned with the specific design of the apparatus thus far referred andere 3 to although it is preferably constructed in accordance with the disclosure of the mentioned Way patent and Wayg et al. application.

The power plant operates substantially as follows: Air enters the'casing I5 at the inlet of the flow passage l2, is compressed by the compressor, and flows into a diffuser or divergent portion Il of the iiow passage which effects a further compression of the air. The compressed air then passes through the openings provided in the walls of the burner tubes 21. The compressed air mixes with the fuel atomized in the tubes by the nozzles 22. The air and fuel mixture is ignated by the spark plugs and burns steadily thereafter. The hot gases or motive fluid comprising the products of combustion and the excess air heated by the combustion on leaving the burner tubes 21 is directed by fixed guide vanes or nozzles 55 of the turbine 2l into the blade passage of the turbine rotor I9. The turbine extracts at least sufilcient energy from the motive fluid to drive the compressor l5, pump I5 and other auxiliary apparatus that may be housed in thejfairing cone i4. The spent gases leaving the turbine are discharged through the propulsion nozzle 23 at a high velocity so that the remaining energy. in the motive fluid is available to propel 'the aircraft. The tailpiece 22 is preferably axially movable with respect to the casing structure so that the back pressure on the turbine and the jet effect produced by the nozzle may be varied.

The present invention is particularly concerned with measuring the speed of rotation o f the turbine and controlling the rate at which fuel is supplied to the burner tubes 21 in order to-maintain the speed of the turbine below a dangerous value.

The speed apparatus may conveniently be housed within a tunnel 4l formed in the top of the casing Il' which also houses lubricating and fuel oil pipes and ignition wires. This apparatus is preferably located in the region enclosed by the small broken rectangle 42 but for clarity it is shown on an enlarged scale above the casing Il with the parts enclosed in a broken rectangle 42a which corresponds to the rectangle 42.

The fuel supply system for the burner tubes comprises the pump i5, which -is ofthe constant displacement type and driven by the turbine so measuring and speed controlling 4 pherlc pressure. Thus the pressure in the fuel supply system fluctuates over a range from near atmospheric pressure to the rated pressure of the pump I5. In the particular. embodiment shown, the maximum pressure necessary for maximum flow through the burner nozzles 'at maximum pressure in the combustion chamber is the maximum rated pressure of the pump. Thus the present speed control device must have a very small total pressure drop as well as be independent of the pressure level.

The Venturi tube 45 satisfies both of these last-mentioned requirements. The total output of the pump passes through the Venturi tube and by measuring the pressure drop from the inlet to the throat of the Venturi tube, which is a function only of thevolume of fuel flowing therethrough. independent of absolute pressure level. a measure of the speed of the turbine shaft is obtained, since the volume output of the constant displacement pump depends only on the rotational speed of the pumpvand also independent of pressure level. This pressure drop in the Ventiiri tub is also used to control the flow of fuel to' the burners, since the speed is dependent on the 'rate at which fuel is supplied so that when th pressure drop reaches a predetermined value. which is basd 'on maximum allowable speed. fuel is by-passed by the control valve from the outlet o f the pump to theV inlet thereof and, in this way, prevents the turbine from exceeding a predetermined speed.- v

The fuel, such as gasoline, for the burner tubes 21 flows fromla suitable tank (not shown) carried by the aircraft, into amain supply pipe 43 to the inlet side 'of the pump l5. The outlet or discharge side -of the pump is connected to a pipe 45, which, in turn. communicates through the Venturi tube 45, with inlet 4l of a four-way, rotary throttle valve, generally indicated 45. One outlet .49 of the valve 4l is connected by a pipe 5l to the manifold pipe 25 of the burner'tubes.

Regulation of the rate of flow of fuel to the burner tubesis eifected'by by-passing more or l'ess` of the fuel from the inlet 41 of the throttle valve to the inlet of the pump by means of a pipe that its output is independent of pressure and depends only on the rotational speed of the turbine shaft, a throttle valve 4l which regulates the amount of fuel going to the burners by bypassing fuel to the inlet sident' the pump, and a control valve 55, which, when open, also -bypasses fuel to the inlet side of` the'pump. The

controlvalve 65 is actuated by the differential in pressure between the inlet and throatbf a Venturi tube 45 which in turn is a measure of the' rate of flow through the Venturi tube and is determined value. It is to beunderstood that the control valve may be actuated by the pressure difference between the throat and exit of the Venturi tube 45, if desired.

The rate of flow to the burners is determined by the pressure drop across the atomizing nozzles. This .pressure drop is controlled by the total 'resistance to flow of the constant volume of fuel output of the pump and is determined by the area of the nozzles plus that of'the throttle valve b!- pass. Absolute pressure in the combustion chamber varies widely depending on operating conditions. that is. pressure ratio and atmos- 52 leading from a second outlet 53 of the throttle valve to the pump inlet pipe 43.

j' The-throttle valve 48 comprises a valve body tn which a rotatable valve member. is received. The valve member 'is rotated. to regulate' the amount of oil owing'to the burners and through Ithe by-pass pipe 52, by any suitable means, for example. the valve member has a pulley 55 connected by a belt 55 to a pulley 51 to which is fixed ahand throttle lever 55. The throttle lever 55 and pulley 51 are located for convenient manipulation by the pilot of the aircraft.

In Fig. 1. the the throttle valve 48 is shown in closed position so that all of the fuel is by-passed or returned to the pump l5 through pipe 52. In this position. a pin 59 carried by wheel 55 engages a stop 5I fixed on the valve body. The valve is fully open when'the pin 59 engagesl a second stop 52 on the valve body. It will be noted that from closed position to full open position of the throttle valve a third outlet 53 of the valve body always remains open.

The outlet 53 is connected by a pipe 54 to the control valve 55, which, in turn, communicates through a pipe 55 and pipes 52and 43 to the inlet of pump I5. It desired the outlet 53 may be dispensed with and pipe 54 connected to the outlet of the Venturi tube 45 by a T connection. The valve 55 is normally closed but is opened, as will appear later, to by-pass fuel flowing into the l throttle valve 48 and thereby reduce the amount of fuel flowing to the burners in the event overand the outlet pipe 86 communicate. A stemmed n valve 89 cooperates with a valve seat 10 in the chamber for controlling the ow through the pipes 84 and 66. The stem 69 of the valve extends into a cylinder 1| formed in the valve body and carries a piston 12. The valve stem 68 is biased to valve closing position by a compression spring 13 acting on the piston.

Since the pressure drop from the inlet to the throat of a Venturi tube is a function only of the rate of ow through the Venturi tube and the ow in the Venturi tube ,46 is dependent on rotational speed of the turbine. this pressure drop is a measure of the rotational speed of the turbine and is used to regulate the supply of fuel to the burners since speed of the turbine is dependent on rate 'at which fuel is supplied to burners to maintain the turbine speed below a predetermined maximum value. 'I'his is done by providing pipes 14 and 15 which connect the inlet 16 and throat 11, respectively. of the Venturi tube with the cylinder 1I at opposite sides of the piston 12.

Thus as the rate of flow of fuel through the Venturi tube increases, the differential in pressure acting on opposite sides of the piston 12 also increases and by selecting a suitable spring 13 the valve 85 may be arranged to begin to open when the speed of the turbine attains a predetermined value. Opening of the valve 65 by-passes fuel from the throttle valve 48 and reduces the amount of fuel going to the burners resulting in a lowering of the turbine speed. As the turbine speed falls off, the rate at which the pump I5 delivers oil also decreases so that the valve 85 tends to reclose until a point of equilibrium is reached.

A pressure gauge 18 connected by means of pipes 19 and 8| to the pipes 1I and 15 may be provided with a scale calibrated in R. P. M. to provide a direct 'indication of the turbine speed. In Fig. 2, there is shown a slightly modified form of control valve 65a in which the piston 12 is replaced by a disc 82 and bellows '83 and 85 are provided on opposite sides of the disc 82. The pipes 15 and 14 extending from the throat 11 and inlet 16, respectively, of the Venturi tube, open to the bellows 88 and 85, respectively. As the pressure within the bellows 85 exceeds the pressure within the bellows 83 by an amount suillcient to deflect the compression spring 13, the valve 85a opens, as in the case of the valve 85, to decrease the supply of fuel to the burners 21; Except for the provision of the bellows the structure of valve 65a may be identical with the valve 55. 'I'he bellows 8l serves tov prevent leakage around the valve stem 69.

While the invention has been shown in several forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof, and it is desired, therefore, that only such limitations shall be placed thereupon as are specifically set forth in the appended claims.

What is claimed is:

1. In apparatus for supplying liquid fuel to a burner or burners to provide heated products of combustion serving as motive fluid to operate a prime mover, a pump operated by the prime mover for supplying liquid fuel at a rate dependent upon prime mover speed; a valve body having a valve chamber and provided with inlet, supply, by-pass, and outlet ports communicating with said valve chamber; a rst conduit connecting said supply port to the burner or burners; a second conduit for supplying fuel from said pump to said inlet port; a third conduit connecting said outlet port with the inlet side of the pump; a fourth conduit providing communication between the by-pass port and the third conduit; a valve for opening and closing the by-pass; means for biasing the valve to closed position; means responsive to the rate at which liquid fuel is supplied to said second conduit to open the valve against the force of the biasing means; a valve in said chamber and movable from the position lapping said supply port with the outlet port open to a position lapping the outlet port with the supply port open and vice versa; and means for moving the lastnamed valve.

2. In apparatus for supplying liquid fuel to a burner or burners to provide heated products of combustion serving as motive fluid to operate a prime mover, a pump operated by the prime mover for supplying liquid fuel at a rate dependent upon prime mover speed; a valve body having a valve chamber and provided with inlet, supply, by-pass, and outlet ports communicating with said valve chamber; a rst conduit1 connecting said supply port to the burner or burners; a second conduit for supplying fuel from said pump to said inlet port; a third conduit connecting said outlet port with the inlet side of the pump; a fourth conduit providing communication between the by-pass port and the third conduit; a valve for opening and closing the by-pass; means for biasing the valve to closed position; means providing a pressure differential which is a function of the rate at which liquid fuel is delivered by the pump to the' REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,446,464 Horvath Feb. 27, 1923 1,713,833 Kochendorfer May 21, 1929 1,886,472 Delaney Nov. 8, 1932 2,280,835 Lysholm Apr. 28, 1942 2,281,411 Campbell Apr. 28, 1942 2,330,558 Curtis Sept. 28, 1943 

